Ultraviolet light wavelength selective filter

ABSTRACT

A wavelength selective filter includes a filter material. The filter material includes a host matrix doped with metal ions. The filter material has a transmission region within a deep ultraviolet (UV) range such that UV light at wavelengths within the transmission region is transmitted through the filter material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to and claims priority benefits from U.S. Provisional Application No. 63/043,089, entitled “Ultraviolet Light Wavelength Selective Filter,” filed 23 Jun. 2020, which is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure generally relate to filtering of light emitted by a light source, and particularly to filtering ultraviolet (UV) light.

BACKGROUND OF THE DISCLOSURE

Many UV light sources emit light at various wavelengths within at least one relatively broad band of wavelengths. Some of the wavelengths are desirable, such as to disinfect the air and/or surfaces within an enclosed space, while other emitted wavelengths are undesirable for interfering with the disinfection or for other reasons. To provide an effective method of disinfection that utilizes these UV light sources, the UV light should be filtered to absorb any undesirable wavelengths and to transmit the desirable wavelengths of light which are needed to kill bacteria and viruses. The desirable wavelengths may be in the deep UV region of the electromagnetic spectrum, which is referred to herein as the region from 190 nanometers (nm) to 280 nm. Most known filters are designed for wavelength regions above 300 nm, and so cannot function to selectively transmit the desirable wavelengths in the deep UV region for disinfection.

One filter designed for the deep UV region is referred to as an interference filter, and is based on a multilayer stack of dielectric materials and metals which create a periodic modulation of the refractive index, resulting in reflection and transmission for certain wavelength ranges in the deep UV. The interference type of filter has several drawbacks. For example, the construction of the interference filter is complex and difficult. The materials are deposited at high temperature and low pressure in precise amounts in order to achieve precise periodic modulation of the refractive index. The interference filter is also known to suffer from relatively low transmission in the bandpass region, which defines the wavelengths permitted to pass through the filter, as well as high dependence on the angle of incidence of light that impinges on the filter. The low transmission in the bandpass region and the high dependence on the angle of incidence are undesirable properties because these properties reduce the amount or rate of desirable UV light that gets emitted from the light source, limiting the disinfection efficacy of the UV light per unit time or energy.

SUMMARY OF THE DISCLOSURE

A need exists for a UV wavelength filter for deep UV light that offers selective filtering to enable a narrow range transmission (or bandpass) region, high transmission in the transmission region, has limited or no angular dependence of incident light, and is less complex and/or costly to manufacture than known filters, such as the interference filter described above. The UV wavelength filter should be selectively designed such that the narrow transmission region encompasses one or more desirable wavelengths and excludes undesirable wavelengths. The desirable wavelengths may be wavelengths associated with disinfection via killing or neutralizing bacteria and viruses.

With those needs in mind, certain embodiments of the present disclosure provide a wavelength selective filter that includes a filter material. The filter material includes a host matrix doped with metal ions. The filter material has a transmission region within a deep ultraviolet (UV) wavelength range such that UV light at wavelengths within the transmission region is transmitted through the filter material.

In one or more embodiments, a method for selectively filtering ultraviolet (UV) light is provided. The method includes doping a host matrix with metal ions to form a filter material that has a transmission region within a deep UV range between about 190 nm and about 280 nm. The metal ions are dispersed within the host matrix. The method includes mounting the filter material on a light source in a light propagation path of light emitted by the light source. The method also includes filtering, via the filter material, the light in the light propagation path such that a first portion of the light having wavelengths within the transmission region is transmitted through the filter material, and a second portion of the light having wavelengths outside of the transmission region is not transmitted through the filter material.

In one or more embodiments, a light source is provided that includes a housing, an origin of light generation held by the housing, and a wavelength selective filter. The origin of light generation is configured to emit ultraviolet (UV) light. The wavelength selective filter is disposed in a light propagation path of the UV light emitted by the origin of light generation. The wavelength selective filter includes a filter material having a host matrix doped with metal ions. The filter material has a transmission region within a deep ultraviolet (UV) wavelength range. A portion of the UV light emitted by the origin of light generation having wavelengths within the transmission region is transmitted through the wavelength selective filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a UV light source that includes a wavelength selective filter according to an embodiment.

FIG. 2 is a diagram showing how the wavelength selective filter can modify the output of a first broadband light source.

FIG. 3 is a diagram showing how the wavelength selective filter can modify the output of a second broadband light source.

FIG. 4 illustrates filter material of the wavelength selective filter according to an embodiment.

FIG. 5 is a diagram showing that two metal ions with different respective absorbance spectrums can be combined within the filter material to achieve regions of high and low absorbance.

FIG. 6 depicts a graph showing an absorbance spectrum of a first filter material.

FIG. 7 depicts a graph showing an absorbance spectrum of a second filter material.

FIG. 8 is a flow chart of a method for selectively filtering UV light according to an embodiment.

DETAILED DESCRIPTION OF THE DISCLOSURE

The foregoing summary, as well as the following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. As used herein, an element or step recited in the singular and preceded by the word “a” or “an” should be understood as not necessarily excluding the plural of the elements or steps. Further, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular condition can include additional elements not having that condition.

Embodiments of the present disclosure provide a wavelength selective filter for UV light. The wavelength selective filter is designed to allow a selected narrow wavelength range of light in the deep UV region (e.g., about 190 nm to about 280 nm) of the electromagnetic spectrum to pass through the filter with high transmission, while absorbing other wavelengths with high optical density so that the other wavelengths cannot pass through the filter. In particular, the embodiments of the wavelength selective filter are useful for turning a broadband (deep) UV light source into a narrowband deep UV light source. Many deep UV light sources produce light at multiple wavelengths throughout the deep UV. For certain applications it is desirable to have the deep UV light source emit only within a narrow wavelength range. One such application is the use of UV light to sanitize and disinfect within an internal cabin of a vehicle, such as an aircraft, or a building, such as a hospital, theatre, commercial business, and the like. The wavelength selective filter can be designed to enable high transmission of wavelengths determined to have antibacterial and antiviral effects without harming human tissue.

The wavelength selective filter can be utilized as a bandpass filter (which absorbs (or blocks) light at wavelengths both above and below a transmission region, referred to as a bandpass region), a bandstop filter (which only absorbs light at wavelengths within the transmission region, referred to as a bandstop region), a shortpass filter (which only absorbs light at wavelengths above the transmission region), or a longpass filter (which only absorbs light at wavelengths below the transmission region). The term transmission region broadly refers to the range of wavelengths of light permitted to pass through the wavelength selective filter according to the embodiments described herein. Depending on the composition of the filter, the filter may be designed as a bandpass filter, a bandstop filter, a shortpass filter, or a longpass filter. References herein to terms such as bandpass region and/or passband region merely refer to the transmission region, and are not intended to limit the application of the wavelength selective filter to use only as a bandpass filter.

The wavelength selective filter according to embodiments herein has a filter material that includes metal ion dopants dispersed within a transparent host matrix. The host matrix in some embodiments is solid, and in other embodiments is liquid. The metal ion dopants have distinguishable inherent absorption bands in the deep UV region, and define at least one transmission or bandpass region in which the metal ions do not absorb the light. The bandpass region is affected by the identities of the metal ion dopants present and the composition of the host matrix. For example, the bandpass region can be tuned during the production of the wavelength selective filter by selecting different metal ions or combinations of metal ions and/or by selecting different compositions of the host matrix.

One or more technical effects of the wavelength selective filter described herein is that the filter is able to selectively transmit a narrow band of wavelengths in the deep UV region and block other wavelengths. As a result, the wavelength selective filter can be coupled to a broadband UV light source to cause the broadband UV light source to operate as a narrowband light source. Furthermore, the wavelength selective filter can be tuned such that the narrow band of wavelengths includes desirable wavelengths, such as wavelengths associated with sanitization and disinfection of air and surfaces without harming human tissue, and excludes undesirable wavelengths. The wavelength selective filter also desirably provides high transmission of the light in the bandpass region, which can improve disinfection efficiency relative to filters that permit less of the disinfecting wavelengths therethrough. The filter material may reduce or limit luminescence, and may have very limited, if any, sensitivity to the angle of incident light, such that the incident angle of light does not affect the intensity or amount of transmitted light through the filter. For these reasons, the wavelength selective filter described herein can outperform other known UV filtering devices. Another technical effect is that the production of the wavelength selective filter may be less complex and less costly than other known UV filtering devices. Furthermore, the optical density of the absorbing regions in the wavelength selective filter can be tuned during production by varying the concentration of metal ion dopants and/or changing the thickness of the filter material, without significant effect on transmission in the bandpass region. For comparison, in order to modify the optical density in an interference filter, additional layers must be added to the filter, which will inevitably reduce transmission in the bandpass region.

FIG. 1 illustrates a UV light source 100 or lamp according to an embodiment. the UV light source 100 includes an origin of light generation 102, a housing 104, and a wavelength selective filter 106. The origin 102 is disposed within a cavity 108 that is defined by the housing 104 and may also be partially defined by the filter 106. The cavity 108 may be filled with gas. The housing 104 may be reflective along an interior surface 110 thereof. The origin 102 may be a bulb, LED, or the like, that generates and emits UV light. The filter 106 is placed in a light propagation path from the origin 102 such that the UV light from the origin 102 directly or indirectly (via reflection) impinges upon an inside surface 112 of the filter 106. The wavelength selective filter 106 allows some of the light rays 114 within a narrow wavelength transmission range (e.g., bandpass region) to transmit through the filter 106 and exit an outside surface 116 of the filter 106 into the surrounding environment. In an embodiment, the filter 106 is a bandpass filter that absorbs light rays 118 that have wavelengths outside of the narrow wavelength transmission region, such that those light rays 118 do not pass through the outside surface 116 into the surrounding environment. The wavelength selective filter 106 is designed to allow a selected narrow wavelength range of light in the deep UV region (e.g., rays 114) to pass through the filter 106 with high transmission, while absorbing other wavelengths of light (e.g., rays 118) with high optical density so that the absorbed light cannot pass through the filter 106. The filter 106 is configured to be transparent to light in the selected wavelength range (e.g., bandpass region). The term transparent as used herein means that at least 60% of the light rays or beams averaged over the selected wavelength transmission region are transmitted through the filter 106. For example, the transmission of light having wavelengths within the transmission region may be less than 100% but greater than 60%, such as around 70%, 80%, or 90%.

A specific application of the wavelength selective filter 106 is the conversion of a deep UV broadband light source into a narrowband light source. For example, the light source 100 may be a broadband deep UV light source, which has its output power centered at one wavelength with a broad distribution of output light around that center wavelength. The broadness of a peak is typically described by its full-width at half-maximum (FWHM). The FWHM of a broadband source in this example is greater than or equal to 5 nm. The light source 100 can represent or include an Excimer lamp such as KrCl or KrBr, a mercury vapor lamp, a deuterium lamp, a xenon lamp, a mercury xenon lamp, a UV LED or UV laser (which uses a phosphor in order to downshift the emission and output light in the deep UV region), an LED with an emission FWHM of 5 nm or more, or the like. Installing the wavelength selective filter 106 on the light source 100 in the propagation path of the emitted broadband light converts the light source 100 to a narrowband light source. The light that exits the filter 106 becomes narrowband in nature.

The effect of our filter on a source of this kind is demonstrated in FIG. 2 , which is a diagram showing how the wavelength selective filter can modify the output of a first broadband light source. FIG. 2 shows a first graph 120 depicting an unfiltered emission spectrum 121 of a broadband deep UV light source, a second graph 122 depicting a transmission spectrum 123 provided by a wavelength selective filter 106 according to an embodiment, and a third graph 124 depicting the resultant output spectrum 125 when the filter 106 is applied in the propagation path of the broadband deep UV light source. The resultant output spectrum 125 shows a relatively narrow bandpass region 126 that extends from about 222 nm to about 245 nm, which represents narrowband deep UV light transmission. The light source 100 shown in FIG. 1 with the filter 106 installed may emit UV light in the spectrum 125 shown in the third graph 124.

In another example, the light source 100 can represent another type of broadband light source in which the unfiltered output light is distributed in multiple peaks centered at different wavelengths. FIG. 3 is a diagram showing how the wavelength selective filter can modify the output of a second broadband light source. FIG. 3 shows how the wavelength selective filter 106 can be placed in the propagation path of such a broadband light source to convert output light to narrowband. For example, FIG. 3 shows a first graph 130 depicting an unfiltered emission spectrum 131 of a broadband deep UV light source, the second graph 122 shown in FIG. 2 depicting the transmission spectrum 123 provided by the wavelength selective filter 106, and a third graph 134 depicting the resultant output spectrum 135 when the filter 106 is applied in the propagation path of the broadband deep UV light source. The output spectrum 135 has a narrow bandpass region 136 that extends from about 228 nm to about 242 nm, which represents narrowband deep UV light transmission.

Referring back to FIG. 1 , the wavelength selective filter 106 includes a filter material 140. The filter material 140 is disposed between the inside and outside surfaces 112, 116 of the wavelength selective filter 106 and is the material that selectively filters the impinging light. FIG. 4 illustrates the filter material 140 according to an embodiment. The filter material 140 includes a host matrix 142 doped with metal ions 144, specifically metal cations. The host matrix 142 is transparent. The metal ions 144 (also referred to as metal ion dopants) are dispersed throughout the host matrix 142.

The metal ions 144 may function as the primary filtering agent. The metal ions 144 may have a valence electron configuration (n−1)d¹⁰ ns², where n represents the principal quantum number of the ion's valence shell, (n−1)d¹⁰ indicates 10 electrons occupying the d orbitals having principal quantum number n−1, and ns² indicates that there are two electrons occupying the s orbital with quantum number n. The metal ions 144 absorb light within specific, inherent absorption ranges based on the elemental compositions. The specific metal ions 144 present in the filter material 140 may be selected based on the absorption ranges in order to control the absorption and bandpass regions of the filter 106. Non-limiting examples of the metal ions 144 can include indium (In⁺), thallium (Tl⁺), tin (Sn²⁺), lead (Pb²⁺), and/or bismuth (Bi³⁺). The filter material 140 may include only a single element (e.g. In⁺) or a combination of multiple different elements (e.g. In⁺ and Sn⁺) for the primary filtering agent. These ions are able to absorb light in certain regions of the deep UV, while being transparent (non-absorbing) in other regions.

FIG. 5 is a diagram showing that two metal ions with different respective absorbance spectrums can be combined within the filter material to achieve regions of high and low absorbance. A first graph 150 depicts the absorbance spectrum 151 of a first metal ion (e.g., metal ion “A”), a second graph 152 depicts the absorbance spectrum 153 of a second metal ion (e.g., metal ion “B”), and a third graph 154 depicts the combined absorbance spectrum 155. The combined absorbance spectrum 155 defines a passband region 156 that is shaped by the absorption ranges of the two metal ions.

In one embodiment, the two metal ions shown in FIG. 5 are combined within the same host matrix 142 (shown in FIG. 4 ). In an alternative embodiment, the wavelength selective filter 106 may be defined by multiple layers of different filter materials in a stack such that the light propagation path travels through the stack. A first layer may include the first metal ion characterized in the first graph 150 dispersed within a host matrix (but not the second metal ion characterized in the second graph 152). The second layer may include the second metal ion characterized in the second graph 152 dispersed within a host matrix (but not the first metal ion). As described herein, the host materials also affect the absorbance and transmission of the filter 106. Thus, a single type of metal ion and combinations of multiple types will result in regions of high transparency and regions of low transparency within the deep UV, enabling the formation and tuning of the wavelength selective filter 106. Absorbance (A) and transmission (T) are related through the equation A=2-log(T), which is the operating principle of the wavelength selective filter 106.

For example, layer ‘A’ might consist of a KBr host matrix and In⁺ metal ion. Layer ‘B’ might consist of a CaCl₂ host matrix with Sn²⁺ and Tl⁺ metal ions. The host matrices of the various layers may be the same or different. Stacking layer A and layer B either directly together, or perhaps with some deep UV transparent material in between, could produce desirable filtering properties. The number of layers could be two, three, four, or the like.

The host matrix 142 is solid in one or more embodiments and liquid in other embodiments. The host matrix 142 is transparent in the portion of the deep UV region where the filter 106 is designed to operate, i.e. it must at least be transparent in the bandpass region(s) of the filter 106. In the embodiments in which the host matrix 142 is solid, the host matrix 142 can include various materials.

In a first solid host embodiment, the host matrix 142 includes an ionic salt containing a halogen anion and an alkali metal or alkaline earth metal cation. The halogen anion may be fluorine, chlorine, bromine, and/or iodine. The alkali metal may be lithium, sodium, potassium, rubidium, and/or cesium. The alkaline earth metal may be beryllium, magnesium, calcium, strontium, and/or barium. The filter material 140 according to a first non-limiting example, is an NaCl host matrix doped with indium (In^(k)) metal ions. The filter material 140 according to a second non-limiting example, includes a first layer having an NaI host matrix doped with thallium metal ions and a second layer having a KBr host matrix doped with tin (Sn) metal ions.

In a second solid host embodiment, the host matrix 142 includes a metal oxide. The metal could be silicon, providing a silicon dioxide host material. For example, the silicon dioxide material could be fused silica, quartz, or fused quartz. In other examples, the metal could be aluminum, hafnium, and/or zirconium.

In a third solid host embodiment, the host matrix 142 includes a nonmetal oxide salt. The nonmetal element may be boron, and the host matrix 142 may be a glass formed from borax, i.e. Na₂[B₄O₅(OH)₄]·8H₂O. In another example, the nonmetal element may be phosphorus, and the host matrix 142 may be a glass formed from NaH₂PO₄.

In a fourth solid host embodiment, the host matrix 142 includes a metal fluoride, with the metal being aluminum, lanthanum, or yttrium. In yet another embodiment, the host matrix 142 includes a metal nitride, such as aluminum nitride or AlGaN.

The metal ions 144 can be incorporated in the solid host matrix 142 during the production of the wavelength specific filter 106 in various ways. In multiple embodiments, the metal ions are initially prepared as a salt with a halogen anion. The salt is referred to as a halide salt of the filtering agent. The halogen anion could be fluorine, chlorine, bromine, or iodine. In a first halide salt embodiment, the solid host matrix is heated above the melting temperature of the host matrix material and the metal ions are incorporated within the melted host matrix. For example, the halide salt of the filtering agent is added in powder form into a container holding the host matrix material, either in bulk form or in powdered form. The container is heated up to or beyond the melting temperature of the host matrix material, allowing the metal ion(s) which are the filtering agent to disperse throughout the host matrix. The mixture is allowed to cool, resulting in the formation of a glassy or crystalline solid comprised mainly of the host matrix material but which also contains the metal ion(s) which are the filtering agent dispersed throughout the matrix. The size and shape of the container, along with the amount of material present in it, will determine the dimensions of the filter material that is produced.

In a second halide salt embodiment, the solid host matrix is not heated above the melting temperature. Instead, the metal ion(s) which are the primary filtering agent can diffuse into the host matrix while the host matrix is below its melting temperature. The halide salt of the filtering agent is added in powder form into a container holding the host matrix material, either in bulk form or in powdered form. The mixture is heated for an extended period of time at a temperature below the melting point of the host matrix material, allowing the metal ion(s) which are the primary filtering agent to diffuse into the host matrix. If the host matrix is in bulk form, then the final shape of the material does not change substantially after this process. If the host matrix is in powdered form, then the material will remain in powdered form after this process. The powdered form can then be mechanically pressed into the desired shape and size.

In a third halide salt embodiment, the halide salt of the filtering agent is co-deposited with the host matrix material during a chemical or physical vapor deposition process.

Other embodiments may forego the preparation of a halide salt of the filtering agent. In one such embodiment, the metal ions of the primary filtering agent are initially prepared in their elemental form and then co-deposited with the host matrix material during a chemical or physical vapor deposition process.

Optionally, a cover material can be applied on at least a portion of the filter material. The cover material may be UV-grade silica or another stable material that is transparent in the deep UV region. The cover material may be applied on the filter material to fully encapsulate the filter material, such as if the filter material is hygroscopic or degrades under ambient environmental conditions (such as alkali halide host matrix), or is a liquid. Another example of a possible cover material is a water-stable metal fluoride, such as MgF₂.

In various other embodiments, the host matrix 142 can be a liquid solution. Suitable liquid host matrices for the wavelength selective filter 106 include water, acetonitrile, cyclohexane, diethyl ether, 1,4-dioxane, ethanol, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, glycerol, heptane, hexadecane, hexane, methanol, methylcyclohexane, pentane, pentyl acetate, 1-propanol, 2-propanol, tetrahydrofuran, and 2,2,4-trimethylpentane. The liquid must be contained by a non-permeable solid material (e.g., container) which is also transparent in the deep UV, to retain the liquid host matrix in place. The solid may be one of the materials described above, such as the cover material or one of the potential solid host matrix materials. In one embodiment, the liquid host matrix may be contained within a container formed by one of the solid host matrices mentioned above that also has metal ion(s) present in it, providing an additional layer of filtering. For example, the metal ions may be present in both the liquid host matrix and the transparent container of the liquid host matrix. Optionally, as described above, a first subset of one or more types of metal ions may be present in the liquid host matrix and a second subset of one or more different types of metal ions may be present in the solid host container.

In multiple embodiments, the liquid host matrix is water. The metal ions may be incorporated by dissolving the metal ions in the form of a salt into the water. The metal ion represents the cation, and the anion could be a halide, perchlorate, or some other compound. Optionally, the oxidation state of the metal ions can be stabilized by an acid or base additive that is added into the solution. In addition, or as an alternative, an electrical potential could be applied to the solution for stabilizing the oxidation state of the metal ions. The absorption regions of the metal ion(s) can be shifted by incorporating another anion in the form of a salt into the solution. It is also possible that a neutral compound, such as 18-crown-6 or ammonia, can act as a ligand to the metal ion, and thus shift the wavelength of absorption. The nature of the additive anion shifts of the absorption region of the metal ions to shorter or longer wavelengths. This enables tunability for the wavelength selective filter 106 in the liquid host embodiments.

Optionally, the liquid filter material 140 (e.g., solvent plus metal ions solution) can be used as a medium for cooling the light source 100. For example, the bulb or other light generation origin 102 may be thermally connected to the liquid filter solution, which enables the solution to absorb heat emitted from the bulb 102. The solvent of the liquid filter solution (such as, but not limited to, water) can serve as a cooling fluid that absorbs and dissipates heat, regulating the temperature of the light source 100 and improving energy efficiency. In a non-limiting embodiment, the liquid filter material 140 can be in direct physical contact with the light generation origin 102 (e.g., bulb) within the cavity 108 in FIG. 1 .

In other embodiments, the liquid host matrix is not water. For example, the halide salt of the metal ions may not be soluble in the non-aqueous liquid host. The metal ion may be prepared with an alternative anion which enhances its solubility in the non-aqueous liquid solvent. A surfactant may be added to facilitate dissolution of the metal ions. A supporting electrolyte with suitable solubility may be added to stabilize the metal ions. In addition, or as an alternative, an electrical potential could be applied to the solution for stabilizing the oxidation state of the metal ions. The filter 106 can be tuned by modifying or changing the anion of the metal ion salt to shift the region of absorption and the bandpass region of no absorption.

The composition of the host matrix, whether solid or liquid, can affect the regions of absorption of the metal ions which act as the primary filtering agent. For example, changing the host matrix material can result in shifting the absorption regions to longer or shorter wavelengths. FIG. 6 depicts a graph 180 showing an absorbance spectrum 182 of a first filter material. FIG. 7 depicts a graph 184 showing an absorbance spectrum 186 of a second filter material. The two graphs 180, 184 show the same wavelength range. The two filter materials have the same types of metal ions. The only difference is that the first filter material has a different host matrix (“Matrix X”) than the second filter material (“Matrix Y”). As shown in FIG. 7 , changing the host matrix from “X” to “Y” shifts the bandpass region 188 from between about 220 nm and about 240 nm to between about 235 nm and about 255 nm. The wavelength selective filter 106 described herein utilizes this operating principle or phenomenon to tune or adjust the bandpass (transparent) and bandstop (absorbing) regions of the filter 106. For example, the identity of the metal ions present and the composition of the host matrix are selected to provide a filter material that has a desired narrowband bandpass region. Thus, if a desirable wavelength of UV light is 250 nm, the host matrix Y in FIG. 7 should be used to permit that designated wavelength through the filter 106. On the other hand, if a desired wavelength is 230 nm, the host matrix X in FIG. 6 should be used.

The desired narrowband bandpass region may represent a narrow range of wavelengths that encompass one or more wavelengths associated with desirable properties, such as effective neutralization of bacteria and viruses without harming human tissue, even during prolonged exposure to the filtered UV light. For example, the filter 106 is tuned such that the emitted UV light exhibits a designated wavelength or narrow wavelength range that is safe (e.g., harmless) for human tissue. For example, the designated wavelength may be 222 nm. Thus, even if the UV light 100 in FIG. 1 persistently emits UV light onto passengers of a vehicle during a trip of the vehicle, such as during a flight of an aircraft, the passengers would be unharmed. The filter 106 absorbs or dissipates wavelengths outside of the designated wavelength or the narrow band such that emitted UV light in the field of illumination only consists of the designated narrowband range of wavelengths.

In a non-limiting example, the designated wavelength is 222 nm. It has been found that sanitizing UV light having a wavelength of 222 nm kills pathogens (such as viruses and bacteria), instead of inactivating pathogens. In contrast, UVC light at a wavelength of 254 nm may inactivate pathogens by interfering with their DNA, resulting in temporary inactivation, but may not kill the pathogens. Instead, the pathogen may be reactivated by exposure to ordinary white light at a reactivation rate of about 10% per hour. As such, UVC light at a wavelength of 254 nm may be ineffective in illuminated areas, such as within an internal cabin of a vehicle. Moreover, UVC light at 254 nm is not recommended for human exposure because it may be able to penetrate human cells. In contrast, sanitizing UV light having a wavelength of 222 nm is safe for human exposure and kills pathogens. Further, the sanitizing UV light having a wavelength of 222 nm may be emitted at full power within one millisecond or less of the UV lamps 120 being activated (in contrast the UVC light having a wavelength of 254 nm, which may take seconds or even minutes to reach full power). In a non-limiting embodiment, the selective wavelength filter 106 is designed to have a narrow bandpass region that encompasses the desired wavelength 222 nm, and has a light blocking (e.g., absorbing) bandstop region that extends from about 225 nm to about 270 nm. Thus, the 222 nm UV light is transmitted through the filter 106 at a high transmittance while 254 nm UV light and other wavelengths in the bandstop region are absorbed and blocked.

The selective wavelength filter 106 may exhibit luminescence upon deep UV radiation, which could be undesirable in certain applications. This luminescence may emit light in the UV-B, UV-A, or visible spectral regions. Various modifications may be made to the selective wavelength filter 106 to reduce or quench luminescence, if desired. For example, luminescence can be downshifted so that the filter luminesces primarily in the visible spectrum (above 400 nm). To accomplish the downshifting, a transition metal ion, or some combination of them, is added to the host matrix, in addition to the metal ions which are the primary filtering agent. Upon UV radiation, the metal ions which serve as the primary filtering agent will absorb some of the incident light, and then transfer that excitation energy to the transition metal ions, which then release the excitation energy in the form of a visible photon. The metal ions could transfer the energy directly (e.g., short range interaction). Or, the UV filters could fluoresce and emit light, and the transition metal ions can reabsorb this light and re-emit downshifted light (e.g., long range interaction). The transition metal ion could be Mn²⁺, which emits around 600 nm. Alternatively, a transition metal with low radiative quantum yield could be chosen in order to reduce the overall amount of luminescence intensity. The emission of visible light could be used as an indicator to the operator of the invention that the filter 106 is under UV illumination. UV illumination is not visible to the human eye and it may not be obvious if a UV light source is On or Off. If the filter 106 is used on a UV light source, it will emit some visible radiation and then user of the UV light source will know that the UV light source is On.

In another embodiment, the luminescence may be quenched by operating the filter 106 at high temperatures. At high temperatures, the absorption and emission bands in the metal ions overlap and cause quenching of the optical emission. In addition, high temperatures promote the occupation of vibrationally excited modes, which tends to increase the rate of non-radiative decay. The heating element that provides the high temperature may be the UV light source itself. Alternatively, a discrete heating element may be intentionally installed on the sides of the filter 106 in order to heat the filter 106 without obstructing the path of light going from the UV source and out of the filter 106.

FIG. 8 is a flow chart 200 of a method for selective filtering of UV light according to an embodiment. The method in various embodiments utilizes and/or provides one or more aspects discussed above in connection with the example wavelength selective filter 106 discussed herein. It may be noted that steps may be added or omitted in various embodiments, and/or various steps may be performed in a different order than shown in FIG. 8 .

At 202, a host matrix is doped with metal ions to form a filter material that has a bandpass region within a deep UV range. The deep UV range may be between about 190 nm and about 280 nm, inclusive of the end values. The metal ions are dispersed within the host matrix as a result of the doping. Optionally, doping the host matrix with the metal ions may include adding a salt that includes the metal ions into the host matrix while heating the host matrix.

Optionally, the host matrix is a liquid. For example, the doping at 202 may include dissolving a salt that includes the metal ions in a water-based solution that represents the host matrix. When the host matrix is a liquid, the method includes, at 204, pouring the host matrix (pre-doping) and/or filter material (post-doping) into a container that is transparent to light in the deep UV range. In embodiments in which the host matrix is not liquid, the step 204 can be omitted.

At 206, the filter material is mounted on a light source in a light propagation path of light emitted by a bulb of the light source. Once in place, at 208, the filter material filters the light in the light propagation path. The filter material may allow transmission of a first portion of the light, having wavelengths within the bandpass region, through the filter material, while blocking transmission of a second portion of the light, having wavelengths outside of the bandpass region, through the filter material. Thus, the filter material enables emission of the first portion of the light through the filter material along the light propagation path, while absorbing or otherwise blocking the emission of the second portion of the light.

The following strategies apply to quench the luminescence in embodiments that utilize a solid host matrix. Non-radiative impurities are (intentionally) introduced into the host matrix to quench the luminescence of the metal ion(s) which serve as the primary filtering agent. The impurity may have the same charge as one of the components in the host matrix, but is a different size. If the host matrix is an alkali halide, the impurity is an alkali metal other than that which constitutes part of the host matrix, or the impurity is a halogen other than that which constitutes part of the host matrix. If the host matrix is an alkaline earth metal halide, the impurity is an alkaline earth metal other than that which constitutes part of the host matrix, or the impurity is a halogen other than that which constitutes part of the host matrix.

Alternatively, the impurity may have a different charge and size from the individual components of the host matrix. If the host matrix is an alkali halide, the impurity may be an alkaline earth metal. If the host matrix is an alkaline earth metal halide, the impurity may be an alkali metal.

In another embodiment, the impurity is an oxygen ion, oxygen gas, or a sulfide ion. The oxide or sulfide compound of the metal ion which serves as the primary filtering agent can be introduced into the host matrix in addition to the halide form of the metal ion, thereby introducing oxide or sulfide ions as impurities to the host matrix.

In another embodiment, the impurity is a metal oxide, or combination of metal oxides, such that the metal(s) would otherwise not be present in the host matrix.

The impurity is water, or some other molecule which is a liquid at room temperature in another embodiment. The impurity could be a derivative of water, e.g. the hydroxide ion (OH⁻).

The luminescence can be quenched by producing a phenomenon known as ‘concentration quenching’, which involves packing the metal ion(s) which serve as the primary filtering agent close together in the solid matrix. The metal ion(s) are used in sufficiently high concentration such that upon absorption of a UV photon, the metal ion is able to transfer its excitation energy to a nearby metal ion. With each successive energy transfer, the probability of encountering a defect in the host matrix increases. Upon encountering a defect, the excitation energy is dissipated without the emission of a photon. Optionally, the metal ion(s) may be intentionally forced to aggregate in the host matrix and form clusters with a high local density of metal ion. This creates the formation of defects in the host matrix, which facilitate quenching of the metal ion(s). Clustering may be induced by using a high concentration of metal ions and/or via the preparation method. The preparation method may include heating the host matrix, applying the metal ions to the host matrix, and then allowing the host matrix to cool slowly, allowing the metal ion(s) to diffuse toward each other as the matrix solidifies.

The following strategies apply for luminescence quenching when the metal ions are dissolved in a liquid matrix. In a first strategy, oxygen gas is intentionally dissolved in the liquid in order to quench the luminescence of the metal ions. The oxygen gas may be introduced into the liquid by using pure oxygen or by using a gaseous mixture which contains some oxygen gas, for example, ambient air. Or, oxygen may be allowed to diffuse into the liquid with a gas permeable separator in the enclosure around the liquid.

In a second strategy with a liquid host matrix, a liquid other than that which comprises the host matrix is mixed into the host matrix in order to quench the luminescence of the metal ions. A third strategy involves adding a surfactant to the host matrix in order to induce aggregation of the metal ions, resulting in concentration quenching.

As described herein, embodiments of the present disclosure provide a filter for selective filtering of deep UV light. The filter can be designed to transmit a narrow range of wavelengths encompassing one or more desired wavelengths, while blocking wavelengths in ranges adjacent to the narrow range. One or more of the desired wavelengths may be utilized to sanitize and disinfect surfaces, air, and people within an internal cabin of a vehicle without harming the people exposed to the UV light.

Further, the disclosure comprises embodiments according to the following clauses:

Clause 1: A wavelength selective filter comprising: a filter material including a host matrix doped with metal ions; the filter material having a transmission region within a deep ultraviolet (UV) range such that UV light within the transmission region is transmitted through the filter material.

Clause 2: The wavelength selective filter of Clause 1, wherein the deep UV range is between about 190 nm and about 280 nm.

Clause 3. The wavelength selective filter of any of Clauses 1 or 2, wherein the transmission region has a width no greater than 30 nm.

Clause 4. The wavelength selective filter of any of Clauses 1-3, wherein the transmission region encompasses a designated wavelength or narrow wavelength range that is safe for human tissue.

Clause 5. The wavelength selective filter of Clause 4, wherein the designated wavelength is 222 nm.

Clause 6. The wavelength selective filter of any of Clauses 1-5, wherein the metal ions includes one or more of thallium, indium, tin, lead, or bismuth.

Clause 7. The wavelength selective filter of any of Clauses 1-6, wherein a location and width of the transmission region along the electromagnetic spectrum is based on an identity of the metal ions and a composition of the host matrix.

Clause 8. The wavelength selective filter of any of Clauses 1-7, wherein the host matrix is solid.

Clause 9. The wavelength selective filter of any of Clauses 1-8, wherein the host matrix is one of an alkali halide, an alkaline earth metal halide, a metal oxide, a metal fluoride, or a metal nitride.

Clause 10. The wavelength selective filter of any of Clauses 1-9, wherein the filter material is a first filter material that defines a first layer, and the wavelength selective filter includes a second filter material that defines a second layer that is stacked with the first layer; the second filter material including a host matrix doped with metal ions, and at least one of the host matrix of the second filter material or the metal ions of the second filter material differs from the first filter material.

Clause 11. The wavelength selective filter of any of Clauses 1-10, wherein the host matrix is liquid.

Clause 12. The wavelength selective filter of Clause 11, wherein the host matrix includes water and an additive to stabilize the metal ions in the water.

Clause 13. The wavelength selective filter of Clause 11, further comprising a container that encapsulates the liquid host matrix; the container being transparent to light in the deep UV range.

Clause 14. The wavelength selective filter of Clause 13, wherein the container is doped with metal ions.

Clause 15. A method for selectively filtering ultraviolet (UV) light; the method comprising: doping a host matrix with metal ions to form a filter material that has a transmission region within a deep UV range between about 190 nm and about 280 nm; the metal ions dispersed within the host matrix; the method comprising: mounting the filter material on a light source in a light propagation path of light emitted by a bulb of the light source, and filtering, via the filter material, the light in the light propagation path such that a first portion of the light having wavelengths within the transmission region is transmitted through the filter material and a second portion of the light having wavelengths outside of the transmission region is not transmitted through the filter material.

Clause 16. The method of Clause 15, wherein doping the host matrix with the metal ions includes adding a salt that includes the metal ions into the host matrix while heating the host matrix.

Clause 17. The method of any of Clauses 15 or 16, wherein doping the host matrix with the metal ions includes dissolving a salt that includes the metal ions in a water-based solution that represents the host matrix.

Clause 18: The method of any of Clauses 15-17, wherein the host matrix is a liquid and the method further comprises pouring the host matrix into a container; the container being transparent to light in the deep UV range.

Clause 19: A light source comprising: housing, a bulb, and a wavelength selective filter; the bulb held by the housing and configured to emit ultraviolet (UV) light; the wavelength selective filter disposed in a light propagation path of the UV light emitted by the bulb; the wavelength selective filter including a filter material having a host matrix doped with metal ions; the filter material having a transmission region within a deep ultraviolet (UV) range; wherein a portion of the UV light emitted by the bulb having wavelengths within the transmission region is transmitted through the wavelength selective filter.

Clause 20: The light source of Clause 19, wherein the transmission region encompasses a designated wavelength or narrow wavelength range that is safe for human tissue

While various spatial and directional terms, such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like can be used to describe embodiments of the present disclosure, it is understood that such terms are merely used with respect to the orientations shown in the drawings. The orientations can be inverted, rotated, or otherwise changed, such that an upper portion is a lower portion, and vice versa, horizontal becomes vertical, and the like.

As used herein, a structure, limitation, or element that is “configured to” perform a task or operation is particularly structurally formed, constructed, or adapted in a manner corresponding to the task or operation. For purposes of clarity and the avoidance of doubt, an object that is merely capable of being modified to perform the task or operation is not “configured to” perform the task or operation as used herein.

As used herein, value modifiers such as “about,” “substantially,” and “approximately” inserted before a numerical value indicate that the value can represent other values within a designated threshold range above and/or below the specified value, such as values within 5%, 10%, or 15% of the specified value.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) can be used in combination with each other. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the various embodiments of the disclosure without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments of the disclosure, the embodiments are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims and the detailed description herein, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.

This written description uses examples to disclose the various embodiments of the disclosure, including the best mode, and also to enable any person skilled in the art to practice the various embodiments of the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments of the disclosure is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if the examples have structural elements that do not differ from the literal language of the claims, or if the examples include equivalent structural elements with insubstantial differences from the literal language of the claims. 

What is claimed is:
 1. A wavelength selective filter comprising: a filter material including a host matrix doped with metal cations, the metal cations including one or more of thallium, indium, tin, or bismuth, the filter material having a transmission region that is within a deep ultraviolet (UV) range and encompasses 222 nm, wherein UV light at wavelengths within the transmission region is transmitted through the filter material.
 2. The wavelength selective filter of claim 1, wherein the deep UV range is between about 190 nm and about 280 nm.
 3. The wavelength selective filter of claim 1, wherein the transmission region has a width no greater than 30 nm.
 4. The wavelength selective filter of claim 1, wherein a location and width of the transmission region along the electromagnetic spectrum is based on an identity of the metal cations and a composition of the host matrix.
 5. The wavelength selective filter of claim 1, wherein the host matrix is solid.
 6. The wavelength selective filter of claim 5, wherein the host matrix is one of an alkali halide, an alkaline earth metal halide, a metal oxide, a metal fluoride, or a metal nitride.
 7. The wavelength selective filter of claim 1, wherein the host matrix is liquid when operable to filter the UV light.
 8. The wavelength selective filter of claim 7, wherein the host matrix includes water and an additive to stabilize the metal cations in the water.
 9. The wavelength selective filter of claim 7, further comprising a container that encapsulates the liquid host matrix, the container being transparent to light in the deep UV range.
 10. The wavelength selective filter of claim 9, wherein the container is doped with a second set of one or more metal cations.
 11. The wavelength selective filter of claim 1, wherein the metal cations in the filter include two different types of metal cations with different respective absorbance spectrums to achieve regions of absorbance above and below the transmission region.
 12. A method for selectively filtering ultraviolet (UV) light, the method comprising: doping a host matrix with metal cations to form a filter material that has a transmission region within a deep UV range between about 190 nm and about 280 nm, the metal cations dispersed within the host matrix, the metal cations including one or more of thallium, indium, tin, or bismuth; mounting the filter material on a light source in a light propagation path of light emitted by the light source; and filtering, via the filter material, the light in the light propagation path such that a first portion of the light having wavelengths within the transmission region is transmitted through the filter material, a second portion of the light having wavelengths below the transmission region is not transmitted through the filter material, and a third portion of the light having wavelengths above the transmission region is not transmitted through the filter material.
 13. The method of claim 12, wherein doping the host matrix with the metal ions includes adding a salt that includes the metal cations into the host matrix while heating the host matrix.
 14. The method of claim 12, wherein doping the host matrix with the metal cations includes dissolving a salt that includes the metal cations in a water-based solution that represents the host matrix when the filter material is operable to filter the light emitted by the light source.
 15. The method of claim 12, wherein the host matrix is a liquid when the filter material is operable to filter the light emitted by the light source, and the method further comprises pouring the host matrix into a container, the container being transparent to light in the deep UV range.
 16. A light source comprising: a housing; an origin of light generation held by the housing and configured to emit ultraviolet (UV) light; and a wavelength selective filter disposed in a light propagation path of the UV light emitted by the origin of light generation, the wavelength selective filter including a filter material having a host matrix doped with metal cations, the metal cations including one or more of thallium, indium, tin, or bismuth, the filter material having a transmission region within a deep ultraviolet (UV) range, the transmission region encompassing 222 nm, wherein a portion of the UV light emitted by the origin of light generation having wavelengths within the transmission region is transmitted through the wavelength selective filter.
 17. The light source of claim 16, wherein the transmission region encompasses a designated wavelength or narrow wavelength range that is safe for human tissue. 